# Non-coherent Detection and Bit Error Rate for an Ambient Backscatter Link in Time-Selective Fading

## TL;DR

This paper introduces a novel non-coherent detection method for ambient backscatter communication over time-selective fading channels, analyzing its bit error rate and robustness, especially with multi-antenna systems and interference mitigation.

## Contribution

It proposes a new receiver architecture based on direct averaging, models the channel as AR process, and derives exact asymptotic BER, advancing the understanding of ambient backscatter detection.

## Key findings

- The new receiver architecture is robust to timing errors.
- Multi-antenna systems can mitigate direct-link interference.
- The analysis provides insights into the impact of angular resolution on BER.

## Abstract

This paper focuses on the non-coherent detection in ambient backscatter communication, which is highly appealing for systems where the trade-off between signaling overhead and the actual data transmission is very critical. Modeling the time-selective fading channel as a first-order autoregressive (AR) process, we propose a new receiver architecture based on the direct averaging of the received signal samples for detection, which departs significantly from the energy averaging-based receivers considered in the literature. For the proposed setup, we characterize the exact asymptotic bit error rate (BER) for both single-antenna (SA) and multi-antenna (MA) receivers, and demonstrate the robustness of the new architecture to timing errors. Our results demonstrate that while the direct-link (DL) interference from the ambient power source leads to a BER floor in the SA receiver, the MA receiver can remove this interference by estimating the angle of arrival (AoA) of the DL. The analysis further quantifies the effect of improved angular resolution on the BER as a function of the number of receive antennas. A key intermediate result of our analysis is the derivation of a new concentration result for a general sum sequence that is central to the derivation of the conditional distributions of the received signal.